Elastomeric polymers such as styrene-butadiene rubbers typically containing 20 to 35% of styrene content are produced in organic solvents such as hexane. These polymers can be terminated with silane containing compounds to yield siloxane end capped polymers. This siloxane termination may also result in an increase in the Mooney viscosity of the treated polymer similar to the increase that occurs during tin coupling. However, upon subsequent desolventization of the siloxane terminated polymer through the use of either steam or heated water, an even larger increase in Mooney viscosity often occurs during the hydrolysis of siloxane groups such as pendant --OR groups on the siloxane end groups thereby leading to coupling via the formation of Si--O--Si bonds between two siloxane end groups.
Thus a process utilizing steam or heated water in the desolventization of siloxane end capped polymers containing hydrolyzable groups such as pendant --OR groups is always accompanied by an increase in the Mooney viscosity of the polymers due to the hydrolysis and subsequent coupling that occurs between the terminal siloxane groups. During this hydrolysis and coupling an undesirable alcohol by-product is also produced. This alcohol by-product can interfere with hexane recycling that must occur in commercial polymerization processes.
It would be extremely desirable to stabilize siloxane terminated polymers to prevent coupling and alcohol formation during desolventization. It is also desirable to retain --OR groups on siloxane terminated polymers during desolventization for subsequent reaction with fillers such as precipitated silica or alumina.